Retigabine (N-[2-amino-4-(4-fluorobenzylamino)phenyl]carbamic acid, ethyl ester] (U.S. Pat. No. 5,384,330) has been found to be an effective treatment of seizure disorders. Bialer, M., et al., Epilepsy Research 1999, 34, 1-41. Retigabine has also been found to be useful in treating pain, including neuropathic and chronic pain. Blackburn-Munro and Jensen, Eur. J. Pharmacol. 2003, 460, 109-116. It also exhibits potent anxiolytic effect in various animal models. Blackburn-Munro, G. et al, CNS Drug Reviews 2005, 11, 1-20.
Benign familial neonatal convulsions, an inherited form of epilepsy, has been associated with mutations in the KCNQ2/3 channels. Biervert, C., et al., Science 1998, 27, 403-06; Singh, N. A., et al., Nat. Genet. 1998, 18, 25-29; Charlier, C., et al., Nat. Genet. 1998, 18, 53-55, Rogawski, Trends in Neurosciences 2000, 23, 393-398. Subsequent investigations have established that the site of action of retigabine is the KCNQ2/3 channel. Wickenden, A. D. et al., Mol. Pharmacol. 2000, 58, 591-600; Main, M. J., et al., Mol. Pharmcol. 2000, 58, 253-62. Retigabine has been shown to increase the conductance of the channels at the resting membrane potential and to bind the activation gate of the KCNQ2/3 channel. Wuttke, T. V., et al., Mol. Pharmacol. 2005, 67, 1009-1017.
The recognition of the site of action of retigabine has prompted a search for other KCNQ 2/3 activators among compounds related to retigabine. WO 2004/058739 describes several compounds in which a thienylmethylamino or benzothienyl methylamino group replaced the 4-fluorobenzylamino group of retigabine; these compounds were reported to be useful as KCNQ 2/3 activators. WO 2004/80950 and WO 2004/82677 describe such compounds where the 4-fluorobenzylamino group of retigabine is replaced by a phenylaminomethyl group. WO 2004/96767 reports compounds which are N-[1-benzyl-4-aminoindol-5-yl]carbamic acid esters. WO 2005/087754 describes a class of reputed KCNQ 2/3 activators that are N-phenyl carbamic acid esters or N-phenyl-amides (for example, N-phenyl acetamides), but in which the central phenyl group lacks an amino group at the 2-position. Typical compounds are N-(2,6-dimethyl-4-(morpholinyl-4-yl)-phenyl)-carbamic acid benzyl ester and 2-cyclopentyl-N-(2,6-dimethyl-4-[2-(4-trifluoromethyl phenyl]-morpholinyl-4-yl)-phenyl)-acetamide.